Here's some info on the newest developments in lasers for DVD...
Japanese Companies Ready Blue-Purple Lasers
May 10, 1999 (TOKYO) -- Several makers in Japan will be ready to supply blue-purple lasers as the light source for next-generation DVDs. Optical disk makers have long been waiting for the technology.
At present, only Nichia Chemical Industries, Ltd. started delivering samples of its blue-purple lasers, having succeeded in producing those with a lifetime of 10,000 hours. Other makers are definitely behind Nichia today, but they are rapidly catching up.
In 1998, for instance, Fujitsu Laboratories Ltd. and Sony Corp. reported that they succeeded in producing a steady-state oscillation of their GaN semiconductor lasers at room temperature and in February 1999 Matsushita Electric Industrial Co., Ltd. followed them.
At the last joint meeting of the Applied Physics Association, Fujitsu Laboratories reported that they succeeded in extending the lifetime, NEC reported their success in the steady-state laser oscillation at room temperature, and Matsushita disclosed a small blue-purple SHG laser.
Steady-State Oscillation for 57 Hours at Room Temperature Fujitsu Laboratories achieved a steady-state oscillation of their GaN blue-purple semiconductor laser for 57 hours at room temperature. Their semiconductor laser was made on a SiC base plate by means of depressurized MOCVD, i.e., the pressure in the chamber was about 13 kPa (100 Torr). Its wavelength is 404 nm, and its maximum power 5 mW. The lifetime that they reported last year was 1 minute.
NEC reported that they obtained a steady-state oscillation of their GaN blue-purple semiconductor laser at room temperature. Their laser was made on an n-type GaN 100 nm thick by means of depressurized MOCVD; the pressure in the chamber was about 13 kPa (100 Torr). Its wavelength is 407.9 nm and its output power has been measured up to 1 mW. They did not disclose its lifetime, saying that it was under measurement.
Improvement of Light Confinement in Lasers
Meijo University and a laboratory of Hewlett-Packard Co. jointly developed a GaN blue-purple semiconductor laser in which the laser beam was confined at a single point. Previously reported blue-purple lasers have several peaks in light intensity distributions. When lasers are used for the optical disk, the newly developed laser
with a single peak intensity improves light efficiency in use compared to those with several intensity peaks only one of which is extracted and focused using a lens.
Nichia disclosed the specifications of their blue-purple semiconductor laser the sample delivery of which started in last February and how they made it. However, the specifications reported were the same that the company reported in last January. the wavelength was about 400 nm; the light output was 5 mW. Its lifetime is 1,000 hours at an operation temperature of +50 degree C although it was estimated to be about 3,000 hours from the slope of increasing the operation current. They guarantee a lifetime of 10,000 hours at an operation temperature of +25 degree C.
GaN Single Crystal 7mm in Diameter
Much attention has been paid to the single crystal technology for GaN in the presentation of blue-purple semiconductor lasers and so on. Because GaN semiconductor lasers can be made by means of homo-epitaxy (a method to grow a crystal on the base plate made of the same material), it is possible to grow a single crystal with a large diameter. The single crystal has less crystal defects and consquently increases the lifetime.
Japan Energy Co. and Yamaguchi University jointly reported that they successfully grew a GaN single crystal 7 mm in diameter. They obtained the single crystal in such a way that Ga was kept for 9 hours in a crucible which was placed in a furnace with N2 gas at 1450 degree C and a high pressure of 10,000 kgW/cm2.
They inspected the surface of the single crystal with a TEM (Transmission-type electron microscope) and detected no crystal defects. They aim at growing far greater single crystal of GaN.
Concerning development of the light source for the next generation DVD, the development of blue-purple SHG (second harmonics generation) lasers is under way in fever pitch, along with blue-purple semiconductor lasers.
Matsushita Electric Industrial disclosed a small blue-purple SHG laser with a dimension of 5 mm x 12 mm x 1.5 mm that was packaged in a case of 16 mm x 7 mm x 3 mm. The wavelength is 426 nm and the light output is 2 mW.
(Nikkei Electronics)
Chris |
